Hi everyone, I am Dennis and I've got a question about group tournaments. I'm in a group (like many others, I presume) and I have received several group tourneys - I decided I wanted to compete in one a week ago or so, but I haven't played it... that's because I have no idea how to compete in it once I say "Join". How do I play a group tourney when I get an invitation in my messages? I'd really like to know.

It sounds like you may have sucessfully signed up for several tournaments!

Click on PLAY -> Tournaments and scroll down to My Upcoming Tournaments to see a list.

However, you may be referring to Team Matches.

There's no simple way of finding which Team Matches you have signed up for, other than going into each of your groups, examining the list of matches, and checking whether you are on the team. 

 There was a useful discussion about this sometime back (http://www.chess.com/forum/view/suggestions/upcoming-matches) but it has unfortunately disappeared.

These other discussions 

group-team-match-monitoring-question

joined-match-list

quotmy-team-matchesquot

limit-on-a-players-max-concurrent-games

list-quotmy-team-matchesquot

looking-up-upcoming-matches

my-team-matches-list

where-are-my-tournaments

     shed some light on the issue.